Photoelectron-fragment ion correlations and fixed-molecule photoelectron angular distributions from velocity imaging coincidence experiments

A new technique, based on velocity imaging, has been developed to examine correlations in energy and angle between the several particles formed in dissociative single and double photoionisation at VUV wavelengths. Electrons and positive fragment ions are imaged in coincidence at position-sensitive detectors; the resulting multidimensional data sets contain separable energy distributions, angular distributions and correlations in energy and angle between the particles. In some cases internal or external evidence indicates that pure axial recoil occurs, without molecular rotation. In such cases fixed-molecule photoelectron angular distributions can be extracted and parametrised. Results for H₂, N₂, NO, CO and O₂ are presented. Effects of shape resonances in the ionisation channels are apparent in several cases.